Method development for determination of (+)‐catechin and (−)‐epicatechin by micellar electrokinetic chromatography: Annual characterization of field grown blackberries

Berries are a rich source of antioxidants compounds, among which is the catechin group. Determination of the monomers (catechin and epicatechin) in fruits is a first step in the way to establish a relationship between polyphenols and their effects on human health. The purpose of this work is to develop a method to determine free catechins in blackberry by MEKC and to characterize levels of catechins in fresh fruits of Rubus fruticosus var. Lochness throughout the annual production period. A methanolic extract was prepared from fresh fruit. Then, it was evaporated and the residue was extracted with diethyl ether. MEKC conditions: phosphoric acid, 30 mmol/L; SDS, 40 mmol/L and triethylamine, 0.1% v/v at pH 2.3; -15 kV of voltage; 10-s hydrodynamic injection; 25°C temperature; and detection at 200 nm. Instrumental and interday precision were lower than 4.7 and 10% RSD, respectively. Only (-)-epicatechin was quantified in blackberries and ranged from 120 to 620 mg/kg fresh weight, which were the lowest values in December and the highest in June. A solid-liquid extraction and an MEKC method were successfully applied to determine (-)-epicatechins in blackberry for the first time. A strong dependence of (-)-epicatechin on the annual average temperature was observed.